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<?php
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/*******************************************************************************
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  NAME                    LAMBERT CYLINDRICAL EQUAL AREA
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  PURPOSE:	Transforms input longitude and latitude to Easting and
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  Northing for the Lambert Cylindrical Equal Area projection.
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  This class of projection includes the Behrmann and
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  Gall-Peters Projections.  The
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  longitude and latitude must be in radians.  The Easting
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  and Northing values will be returned in meters.
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  PROGRAMMER              DATE
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  ----------              ----
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  R. Marsden              August 2009
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  Winwaed Software Tech LLC, http://www.winwaed.com
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  This function was adapted from the Miller Cylindrical Projection in the Proj4php
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  library.
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  Note: This implementation assumes a Spherical Earth. The (commented) code
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  has been included for the ellipsoidal forward transform, but derivation of
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  the ellispoidal inverse transform is beyond me. Note that most of the
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  Proj4php implementations do NOT currently support ellipsoidal figures.
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  Therefore this is not seen as a problem - especially this lack of support
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  is explicitly stated here.
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  ALGORITHM REFERENCES
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  1.  "Cartographic Projection Procedures for the UNIX Environment -
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  A User's Manual" by Gerald I. Evenden, USGS Open File Report 90-284
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  and Release 4 Interim Reports (2003)
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  2.  Snyder, John P., "Flattening the Earth - Two Thousand Years of Map
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  Projections", Univ. Chicago Press, 1993
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 ****************************************************************************** */
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/**
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 * Author : Julien Moquet
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 *
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 * Inspired by Proj4php from Mike Adair madairATdmsolutions.ca
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 *                      and Richard Greenwood rich@greenwoodma$p->com
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 * License: LGPL as per: http://www.gnu.org/copyleft/lesser.html
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 */
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class Proj4phpProjCea {
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    /* Initialize the Cylindrical Equal Area projection
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      ------------------------------------------- */
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    public function init() {
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        //no-op
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    }
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    /* Cylindrical Equal Area forward equations--mapping lat,long to x,y
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      ------------------------------------------------------------ */
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    public function forward( $p ) {
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        $lon = $p->x;
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        $lat = $p->y;
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        /* Forward equations
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          ----------------- */
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        $dlon = Proj4php::$common->adjust_lon( $lon - $this->long0 );
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        $x = $this->x0 + $this->a * $dlon * cos( $this->lat_ts );
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        $y = $this->y0 + $this->a * sin( $lat ) / cos( $this->lat_ts );
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        /* Elliptical Forward Transform
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          Not implemented due to a lack of a matchign inverse function
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          {
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          $Sin_Lat = sin(lat);
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          $Rn = $this->a * (sqrt(1.0e0 - $this->es * Sin_Lat * Sin_Lat ));
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          x = $this->x0 + $this->a * dlon * cos($this->lat_ts);
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          y = $this->y0 + Rn * sin(lat) / cos($this->lat_ts);
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          }
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         */
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        $p->x = $x;
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        $p->y = $y;
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        return $p;
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    }
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    /**
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     * Cylindrical Equal Area inverse equations--mapping x,y to lat/long
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     *
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     * @param type $p
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     * @return type
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     */
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    public function inverse( $p ) {
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        $p->x -= $this->x0;
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        $p->y -= $this->y0;
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        $p->x = Proj4php::$common->adjust_lon( $this->long0 + ($p->x / $this->a) / cos( $this->lat_ts ) );
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        $p->y = asin( ($p->y / $this->a) * cos( $this->lat_ts ) );
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        return $p;
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    }
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}
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Proj4php::$proj['cea'] = new Proj4phpProjCea();